Barrow Haze

A malevolent fog created from grave mould springs into existence at a point you can see, filling a 10ft-radius area with the stench of decay and the chill of the grave, strengthening the power of Necromancy.

When you cast this spell you may choose either of the following effects, which will persist until the spell ends: 

When you cast a Necromancy spell while Barrow Haze is in effect, you can choose any square within the fog as its point of origin, and for the purposes of casting the spell you count as being able to see from any point within the fog.

OR

Undead creatures under your command within the fog gain the Undead Fortitude feature if they do not already possess it, and gain Advantage on attack rolls against other creatures within the fog.

When cast at higher levels, you may expand the radius of the fog by 10ft per additional level of spell slot used, ie casting Barrow Haze using a 3rd-level spell slot increases the radius of the fog to 20ft, while using a 4th-level spell slot increases the radius to 30ft.

When cast using a 5th-level spell slot or higher, you can choose one of the below effects in addition to one of the existing effect choices:

Creatures within the fog roll their saving throws with disadvantage against any Necromancy spell you cast when the target creature or area is within the fog.

OR

Undead creatures under your control within the fog gain the effects of the Heroism spell.